Flexible photovoltaic module

ABSTRACT

A flexible and/or bendable photovoltaic (PV) module including a plurality of PV cell based units, the immediately-adjacent of which are chained together by a flexible joint. A segment of flexible electrically-conductive member runs through the flexible joint to establish electrical communication between the PV cell based units. An encapsulant embedding the PV cell based units optionally defines a convex surface above a PV cell. A PV cell based unit may include a hologram increasing the amount of light delivered to the PV cell.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from and benefit of the U.S. Provisional Patent Applications Nos. 61/559,980 titled “Flexible Crystalline PV Module Configurations” and filed on Nov. 15, 2012; Nos. 61/559,425 filed on Nov. 14, 2011 and titled “Advanced Bussing Options for Equal Efficiency Bifacial Cells”; 61/560,381 filed on Nov. 16, 2011 and titled “Volume Hologram Replicator for Transmission Type Gratings”; and 61/562,654 filed on Nov. 22, 2011 and titled “Linear Scan Modification to Step and Repeat Holographic Replicator”. The disclosure of each of the above-mentioned provisional applications is incorporated herein by reference in its entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The present invention was made with government support under HR0011-11-C-0040 awarded by the Defense Advanced Research Projects Agency (DARPA). The government has certain rights to the invention.

TECHNICAL FIELD

The present invention relates to photovoltaic cells and more specifically to flexible photovoltaic modules employing such cells.

BACKGROUND OF THE INVENTION

Solar energy will satisfy an important part of future energy needs. While the need in solar energy output has grown dramatically in recent years, the total output from all solar installations worldwide still remains around 7 gigawatts, which is only a tiny fraction of the world's energy requirement. High material and manufacturing costs, low solar module efficiency, and shortage of refined silicon limit the scale of solar power development required to effectively compete with the use of coal and liquid fossil fuels.

The key issue currently faced by the solar industry is how to reduce system cost. The main-stream technologies that are being explored to improve the cost-per-kilowatt of solar power are directed to (i) improving the efficiency of solar cells that comprise solar modules, and (ii) delivering greater amounts of solar radiation onto the solar cell. In particular, these technologies include developing thin-film, polymer, and dye-sensitized photovoltaic (PV) cells to replace expensive semiconductor material based solar cells, the use of high-efficiency smaller-area photovoltaic devices, and implementation of low-cost collectors and concentrators of solar energy.

While the reduction of use of semiconductor-based solar cells is showing great promise, for example, in central power station applications, it remains disadvantageous for residential applications due to the form factor and significantly higher initial costs. Indeed, today's residential solar arrays are typically fabricated with silicon photovoltaic cells, and the silicon material constitutes the major cost of the module. Therefore techniques that can reduce the amount of silicon used in the module without reducing output power will lower the cost of the modules.

The use of devices adapted to concentrate solar radiation on a solar cell is one such technique. Various light concentrators have been disclosed in related art, for example a compound parabolic concentrator (CPC); a planar concentrator such as, for example, a holographic planar concentrator (HPC) including a planar highly transparent plate and a holographically-recorded optical element mounted on its surface; and a spectrum-splitting concentrator (SSC) that includes multiple, single junction PV cells that are separately optimized for high efficiency operation in respectively-corresponding distinct spectral bands. A conventionally-used HPC is deficient in that the collection angle, within which the incident solar light is diffracted to illuminate the solar cell, is limited to about 45 degrees. Production of a typical SSC, on the other hand, requires the use of complex fabrication techniques.

Another area which contributes to the cost of PV material is the use of mono crystalline and multi-crystalline silicon. While offering higher conversion efficiencies as compared to thin film material, the rigid nature of the crystalline and multi-crystalline silicon causes the PV material to crack or break when flexed. Due to the conventional bussing in a cell, if an area which is not in contact with the busbar separates from the cell, it no longer contributes to the cell's output. Since most PV systems are connected in a serial connection, each broken cell further limits the current of the serially connected string. The high rate of cell breakage greatly increases the costs associated with manufacturing and transporting conventional PV cells.

SUMMARY OF THE INVENTION

The present invention addresses the need for flexibility of PV modules and greatly diminishes the problems associated with cell breakage. Due to their flexible structure, the PV module embodiments can be transported at lower operational cost as compared to the conventional PV modules.

Embodiments of the invention provide a flexible photovoltaic (PV) module that includes a plurality of PV cell based units, each unit containing a corresponding PV cell; and a flexible joint connecting a pair of immediately adjacent PV cell based units from this plurality. The module further includes an electrically-conductive member electrically connecting the pair of immediately adjacent PV cell based units and passing through the flexible joint. In a specific embodiment the electrically-conductive member includes a flexible conductive tape. At least one of the PV cell based units may additionally includes a first rigid layer disposed substantially parallel to a surface of the corresponding PV cell such as to increase rigidity of a portion of the module where the PV cell is disposed.

An embodiment of the module may include an optically transparent protective material embedding a pair of immediately adjacent PV cell based units and the flexible joint connecting such pair. Optionally, a portion of such optically transparent material covering a PV cell based unit has a non-uniform thickness across the PV cell unit. Optionally, an outer surface of a portion of such optically transparent material forms a dome over a corresponding PV cell based unit. In a specific embodiment, the dome has a curvature that changes across the surface of the dome. Alternatively or in addition, the optically transparent material has a first surface that is substantially parallel to a surface of a PV cell, and the flexible joint may include a second surface that is inclined with respect to the first surface. The first and second PV cells of the PV cell based module may be electrically connected with parallel bussing. A PV cell based module may include a hologram.

Embodiments of the invention further provide a flexible photovoltaic (PV) module that includes (i) a plurality of PV cell based units, each unit containing a corresponding PV cell; (ii) a flexible joint connecting immediately adjacent PV cell based units from the plurality of units, with flexible joint having a surface that is inclined with respect to a surface of a PV cell; and (iii) an electrically-conductive member electrically connecting the immediately adjacent PV cell based units, the member passing through the flexible joint. The module optionally contains an optically transparent protective material embedding the immediately adjacent PV cell based units and the corresponding flexible joint such as to define a convex surface substantially centered with respect to a PV cell based unit. The convex surface may have a curvature parameter that is variable across said convex surface. At least one of the PV cell based units optionally includes at least one of a first rigid layer disposed substantially parallel to a surface of the corresponding PV cell and a hologram.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a holographic planar concentrator;

FIG. 2A shows an embodiment of a holographic spectrum-splitting device;

FIG. 2B shows an alternative embodiment of a holographic spectrum-splitting device;

FIG. 3 is a schematic of a flexible PV module of the present invention;

FIG. 4A is a block diagram illustrating an embodiment of a flexible PV module laying flat;

FIG. 4B is an alternative depiction of the embodiment of FIG. 4A, in side view, wherein the flexible joints are bent;

FIG. 5A is a block diagram of an alternate embodiment of the flexible PV module with a flexible joint employed at every third PV cell;

FIG. 5B is an alternative depiction of the embodiment of FIG. 5A wherein the flexible joints are bent;

FIG. 6 is a block diagram of an embodiment with redundant bussing;

FIG. 7 is a block diagram of an embodiment having an USB Plug;

FIG. 8 is a flowchart of an example method for fabrication of a flexible PV module according to an embodiment of the invention;

FIG. 9 shows one embodiment of Applicants' solar module having angled joints to enhance total internal reflectance (TIR);

FIG. 10 shows a view of a portion of the embodiment of FIG. 9.

FIGS. 11 and 12 show an embodiment of a solar module having a curved surface topography on the upper surface and a flat-and-angled-surface topography at the lower surfaces.

DETAILED DESCRIPTION

References throughout this specification to “one embodiment,” “an embodiment,” “a related embodiment,” or similar language mean that a particular feature, structure, or characteristic described in connection with the referred to “embodiment” is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. It is to be understood that no portion of disclosure, taken on its own and in possible connection with a figure, is intended to provide a complete description of all features of the invention.

In addition, the following disclosure may describe features of the invention with reference to corresponding drawings, in which like numbers represent the same or similar elements wherever possible. In the drawings, the depicted structural elements are generally not to scale, and certain components are enlarged relative to the other components for purposes of emphasis and understanding. It is to be understood that no single drawing is intended to support a complete description of all features of the invention. In other words, a given drawing is generally descriptive of only some, and generally not all, features of the invention. A given drawing and an associated portion of the disclosure containing a description referencing such drawing do not, generally, contain all elements of a particular view or all features that can be presented is this view, for purposes of simplifying the given drawing and discussion, and to direct the discussion to particular elements that are featured in this drawing. A skilled artisan will recognize that the invention may possibly be practiced without one or more of the specific features, elements, components, structures, details, or characteristics, or with the use of other methods, components, materials, and so forth. Therefore, although a particular detail of an embodiment of the invention may not be necessarily shown in each and every drawing describing such embodiment, the presence of this detail in the drawing may be implied unless the context of the description requires otherwise. In other instances, well known structures, details, materials, or operations may be not shown in a given drawing or described in detail to avoid obscuring aspects of an embodiment of the invention that are being discussed. Furthermore, the described single features, structures, or characteristics of the invention may be combined in any suitable manner in one or more further embodiments.

Moreover, if the schematic flow chart diagram is included, it is generally set forth as a logical flow-chart diagram. As such, the depicted order and labeled steps of the logical flow are indicative of one embodiment of the presented method. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated method. Additionally, the format and symbols employed are provided to explain the logical steps of the method and are understood not to limit the scope of the method. Although various arrow types and line types may be employed in the flow-chart diagrams, they are understood not to limit the scope of the corresponding method. Indeed, some arrows or other connectors may be used to indicate only the logical flow of the method. For instance, an arrow may indicate a waiting or monitoring period of unspecified duration between enumerated steps of the depicted method. Without loss of generality, the order in which processing steps or particular methods occur may or may not strictly adhere to the order of the corresponding steps shown.

The invention as recited in claims appended to this disclosure is intended to be assessed in light of the disclosure as a whole, including features disclosed in prior art to which reference is made.

An HPC 100, shown schematically in a cross-sectional view in FIG. 1, typically includes a highly-transparent planar substrate 104 of thickness d (such as, for example, substrate made of glass or appropriate polymeric material having the refractive index n₁) at least one diffractive structure 108, having width t, at a surface of the substrate 104. Such diffractive structure may include, for example, a holographic optical film (such as gelatin-on-PET film stack) in which a plurality of multiplexed diffraction gratings have been recorded with the use of laser light. The diffractive structure 108 can be optionally capped with a protective cover layer (not shown). The substrate 104 is typically cooperated with a solar-energy-collecting device 112 such as a PV cell. The diffractive structures 108 diffract wavelengths usable by the PV cell 112, while allowing the light at unusable wavelength to pass through, substantially unabsorbed. The usable energy is guided via the total internal reflection at the glass/air or glass/cover interface to strings of solar cells, resulting in up to a 3× concentration of solar energy per unit area of PV material.

As shown in FIG. 1, the PV cell 112 of width T is juxtaposed with the second surface of the substrate 104 in opposition to the diffractive structures 108 and in such orientation that ambient (sun-) light I, incident onto the structure 108 at an angle θ₁, is diffracted at an angle θ_(D) onto the cell 112 either directly or upon multiple reflections within the substrate 104. To estimate the range of incident angles (that would produce the diffracted light intersecting the surface of the PV cell 112) for different parameters of the HPC 100, such as substrate thickness, the displacement of the PV cell 112 with respect to the edge of the grating 108, or other geometrical parameters, one can use the grating equation. For example, for a glass substrate 104 and when t=T=d, the range of incident angles (the collection angle) at which the cell 112 is illuminated is about 45 degrees. When t=2T=2d, the collection angle is reduced to about 38 degrees. The angular range within which the corresponding diffracted light is produced is about 10° to 15° for most of the wavelengths. However, the angle-wavelength matching can be used to extend this range for different portions of the available spectral bandwidth of the HPC 100.

The increase in PV-conversion efficiency, in comparison with a use of a conventional PV-cell, is also achieved by using multiple junction cells that create electron-hole pairs at the expense of energy of incident light over a wider spectral range than a single junction cell. The use of holographic grating with such spectrum-splitting devices (SSD) also offers some advantages. The hologram can be designed to diffract light within a specific spectral band in a desired direction (for example, towards one PV-cell) and be multiplexed with another hologram that diffracts light of different wavelength in another direction (for example, towards another PV-cell). One example of such holographic SSD 200, shown in FIG. 2A, includes two holographically-recorded diffractive structures 204 and 208 that are cascaded at a surface 212 of the substrate 216 (i.e., at the input of the SSD 200) and that diffract light of different wavelengths. For example, the upper hologram 204 diffracts light at wavelength λ₁ longer than wavelength λ₂ diffracted by the hologram 208. A long-wavelength PV cell 214, corresponding to hologram 204, and a short-wavelength PV cell 218, corresponding to hologram 208, are positioned transversely with respect to the holograms 204, 208 (as shown, at side facets of the substrate 216). Directionally-diffracted towards target PV cells, light 224, 228 reaches the PV cells via reflections off the surfaces of the substrate 216. A simple light-concentrating reflector can additionally be used. A similar SSD 230, upgraded with cylindrical parabolic reflectors 234, 238 that guide the diffracted light towards target PV cells, is depicted in FIG. 2B. In both cases, the collection angle is determined by geometry of the system and the diffraction characteristics of the holograms.

The present invention is directed to a flexible PV module optionally employing a crystalline PV material (which possesses high module solar-energy conversion efficiency). More specifically, the presently disclosed flexible PV module designs utilize a PV material without the use of conventional conductive buss-bars on the PV cell. Rather, the discussed embodiments call for the novel use of a conductive tape and redundant exterior bussing, thereby simplifying the PV-module structure that now requires only conductive members between the individual PV cells. Furthermore, the resulting embodiments are sealed to substantially isolate them from the environment and can be used in applications that require flexible, highly efficient and readily transportable modules. With the use of additional framing, the discussed modules can further be rigidly set-up in a substantially the same way as the conventional crystalline modules. Such framing is removable and allows for easy transportation of the modules.

Turning now to FIG. 3, a diagram is presented illustrating an embodiment 300 of the flexible PV module according to the invention. The module 300 includes multiple (repeated in the structure 300) PV-cell-based units shown as four units 302(a-d), wherein each PV-cell-based repeat unit 302(a-d) may be configured as described in reference to FIGS. 1-2B. The immediately adjacent repeat units 302(a-d) are separated by a distance n from one another and electrically connected via flexible electrically-conducting member 310(a-d). Each of the flexible members or connectors 310(a-d) preferably includes conductive tape. In related implementations, other flexible electrically-conductive members can be used such as, and without limitation, conductive epoxy, flat wire, flat stranded wire, flat PV wire with solder, a conductor with a flexible mechanical joint, or a small gauge electrical wire.

As is shown in FIG. 3, each individual flexible electrical conductor 310(a-d) electrically connects a first surface of the PV material of a first PV-cell-based unit with a second surface of the PV material of a second PV-cell-based unit. More specifically, looking at PV cell based units 302(a) and 302(b), the conductor 310(b) electrically connects the first surface 301(a) of PV material 303(a) with the second surface 305(b) of PV material 303(b). Likewise, PV cell based units 302(b) and 302(c) are electrically connected via conductor 310(c) which electrically connects the first surface 301(b) of PV material 303(b) with the second surface 305(c) of PV material 303(c). PV cell based units 302(c) and 302(d) are likewise electrically connected via the conductor 310(d). This sequential design allows the conductors 310(a)-(d) to operate as electrically conductive fingers between PV cell based units 302(a)-(d). As explained below, such electrical connection together with the use of redundant exterior bussing substantially negates the need in using conductive buss-bars in juxtaposition with the PV material, as commonly done in PV-module designs of related art.

As an electrical conductor 310(a-d) is configured to be flexible, its use for operable connection of the immediately adjacent PV-cell-based units further creates flexible joints 308(a-d) that are, as a result, bendable. As illustrated, each joint 308(a-d) bridges the distance n between the immediately adjacent cells. In one embodiment n is about 3 mm, and in a related embodiment n is about 8 mm. In other embodiments, n may be less than 3 mm or more than 8 mm depending on the desired radius of bend of a given joint. As will be appreciated by one of ordinary skill in the art, the bend radius is inversely proportional to the length of the flex joint and thus smaller bend radii can be achieved with the use of longer flex joints. In yet other embodiment, the distances between different pairs of immediately adjacent cells are not the same.

When a conductive tape is used to form a flexible electronic conductor 310(a-d), such tape may include metallic foil such as, and without limitation, the foil containing copper, tin-plated copper, aluminum, or a combination thereof. Alternatively or in addition, the conductive tape may further include an adhesive material (such as, and without limitation, acrylic and silicone) and a liner. The adhesive material, in turn, may posses electrical conductivity to establish a current path from each of the PV cell based units 302(a-d) to the foil component of the conductive tape 310(a-d).

While not immediately apparent, it is important to recognize that the use of flexible electronic connector(s) 310(a-d) in the present embodiments brings to light an unexpected advantage of the resulting structure over structures of the related art and enables the embodiments of the invention to avoid important operational deficiencies that otherwise would exhibit themselves if the PV-cell-based units 302(a-d) did not possess the flex-joint but, for example, were simply soldered together instead. In particular, in addition to lacking flexibility, the soldered to one another PV cell based units inevitably mechanically stress the substrate material and create micro-cracks due to the different thermal expansion rates of the soldering material and the silicon elements.

In the module 300, each PV cell based unit 302(a-d) is optionally structurally protected with at least one substantially rigid layer, such as a layer 304(a-d) and/or a layer 306(a-d), which may have substantially equal or different lengths, as illustrated in FIG. 3. In such embodiment, rigid layers 304(a-d) and/or 306(a-d) structurally reinforce PV cell based units 302(a-d) thereby preventing the module 300 from flexing at any point along and within the bounds of an individual PV cell based unit 302(a-d) and thereby causing damage to the PV cells of these units. In the embodiment depicted in FIG. 3, each PV cell based unit 302(a-d) is reinforced with by both an upper rigid layer 304(a-d) and a lower rigid layer 306(a-d). In another embodiment (not shown), at least one PV cell based unit 302(a-d) is protected by only one rigid layer or, in addition or alternatively, by more than two rigid layers. In a related embodiment, the number of rigid layers protecting each PV cell based unit 302(a-d) varies across the module 300. In such embodiment, more rigid layers may be used to protect the PV cell based units. In a specific embodiment, a rigid reinforcing layer 304(a-d), 306(a-d) is longer than a corresponding PV cell based unit.

Layers 304(a-d) and 306(a-d) can be made from the same or different materials, such as rigid polymer or plastic (optionally translucent or transparent), for example. In one implementation, one or both of layers 304 and 306 include a thermoplastic such as, and without limitation, polycarbonate, and/or ionomer (including, for example and without limitation, poly(ethylene-co-methacrylic acid) or chemically curable plastic such as, for example, ethylene vinyl acetate.

The module 300 further includes a protective material or encapsulate 312. Like the connector 310(a-d), the material 312 is configured to be flexible and, therefore, does not detract from the flexibility of joints 308(a-d). The material 312 adds another operational advantage to the units 302(a-d) by sealing each unit and isolating it from corrosive and otherwise damaging elements of the environment. The material 312 may be configured, in reference to the PV material 303(a-d) as an overlayer, an under layer, and/or both. The material 312 optionally encapsulates all of the PV cell based units 302(a-d), rigid layers 304(a-d) and 306(a-d), and connectors 310(a-d). In certain embodiments, material 312 is a thermoplastic such as, and without limitation, a UV stable Polyethylene Terephtalate (PET), or Surlyn® by DuPont™.

FIGS. 4A, 4B are diagrams schematically and without limitation illustrating the operationally flexible configuration of the embodiment 300 of FIG. 3. In FIG. 4A a block diagram of a PV module 400 is shown, in top few, stretched out flat. The black bars represent PV-cell-based units and the dashed lines denote flexible joints between the immediately adjacent PV cell based units. A side view of PV module 400 is shown in FIG. 4B wherein a PV module is depicted flexed along each of the horizontal joints to partially roll in on itself.

In alternate embodiments of Applicants' flexible PV module, the flexible joints may be strategically positioned between predetermined immediately adjacent PV cell based units and not between other units. By way of example and not limitation, flexible joints may be positioned at every third PV-cell-based unit, as shown in FIGS. 5A, 5B. Here, the black bars represent PV cell based units and the dashed lines denote the flexible joints configured as every third PV cell based unit. In certain embodiments, a distance between the immediately adjacent PV cell based units that are connected by a flexible electrically-conductive joint may be greater or shorter than the distance between PV cell based units which are not connected by such joint. In such embodiments, the immediately adjacent PV cells without a joint therebetween may be simply joined using a conductive tape or any other well known material for joining PV cells. However, the lack of a flex joint and the rigidity of the joining material is likely to prevent flexing between such PV-cell units.

Optionally, the PV cell based units used in an embodiment of a flexible PV module are cut smaller than conventionally used PV-cell-based units. For example, a full-sized PV-cell-based unit may be about 4×4 in², 5×5 in², or 6×6 in². The diced PV cell based units are a subset of these full sized PV cell based units. For example, a full sized PV cell based unit of 4×4 in² may be diced into four smaller PV cell based units of 2×2 in² each. Alternatively, the full sized PV cell based unit may be diced into two smaller PV cell based units of 2×4 in² each. Despite the apparent increase in complexity of structure composed of such diced units, and contrary to the expectation of the increased cost of manufacture, this counterintuitive use of the smaller units substantially increases the overall flexibility of the PV module and reduces impact-related shattering, thereby increasing the life-time and the operational costs of the PV module. In certain embodiments, the size of each PV module may vary, as is further illustrated in FIG. 5A wherein PV cell based units 502(a), (d), (e), and (h) are larger than PV cell based units (b), (c), (f), and (g).

Turning now to a block diagram of FIG. 6, multiple flexible PV modules may be arranged and operably connected in parallel strings, for example as array 600. While the array 600 is shown comprising only two parallel internal PV strings, one of ordinary skill will appreciate that FIG. 6 is illustrative and that arrays comprising more module are considered within the scope of the present invention. Arrays with fewer PV strings may be used for applications such as portable electronic charging, while arrays with more PV strings may be used for providing electrical power to applications having greater power demands (such as, for example powering the operating refrigerator).

As can be seen in FIG. 6, the flexible joints of the array 600, denoted by the dashed lines 610, are arranged in both the vertical and horizontal directions. Thus, the depicted exemplary array 600 is enabled to flex in both the vertical and horizontal directions. In certain embodiments, the return wire pathway may also be flexible so as not to restrict the overall flexibility of the array.

Additionally, as shown in FIG. 6, the external parallel connected bussing on the array 600 provides redundant electrical circuits 620 for added module reliability. As a result, damage to one individual module of the array 600 substantially does not affect the output received from the other individual modules.

In one implementation, either of or both the negative lead 630A and positive lead 630B on an array 600 can operably connected with an appropriate USB (Universal Serial Bus) plug housing to provide charging for USB compatible devices, such as, and without limitation, cellular phones, tablets, and battery chargers. A block diagram of such an embodiment is provided in FIG. 7 as an array 700 having the USB plug 710.

An embodiment of a method for fabrication of a flexible (crystalline) PV module array is discussed in reference to a flowchart of FIG. 8. At step 802, the PV cell based units are arranged into a desired formation such as, for example, a string or an array. Once arranged, the PV cell based units are operably equipped with an electrical buss made of a material suitable for creating a flexible joint, as depicted at step 804. The PV cell based units are preferably bussed using charge tape (however other flexible conductive material can be used, such as, for example, conductive epoxy, flat wire, flat stranded wire, flat PV wire with solder, or a conductor with a flexible mechanical joint). In certain embodiments, electrical terminals can be added during the process of adding the buss to the PV cell based units.

The material layers of the bussed PV cell based units are then stacked in the appropriate order, at step 806. In one embodiment, the material layers are stacked as follows: (1) a first protective layer, (2) a first encapsulant layer, (3) a bussed PV cell based unit, (4) a second encapsulant layer, and (5) a second protective layer. In a related embodiment, additional material layers may be added. In yet other embodiments, the protective layers or encapsulant layers may not be used. The protective layer may include PET and/or a custom cut glass product such as, for example, an alkali-aluminosilicate glass sheet. A liquid encapsulant may introduced into the mold and over the individual solar cells and allowed to harden. In some embodiments, heat is applied to chemically set the liquid or to otherwise harden the liquid to form a solid that fully encapsulates the solar cells. In one embodiment, the liquid encapsulant includes two components that chemically react to form a solid material (such as, for example, a two-part epoxy).

Once the material layers are stacked, the overall stack is laminated or fused together, at step 808. In certain embodiments a vacuum hot lamination process is used. In such embodiments, the cycle times and temperatures are adjusted based on the encapsulating material used. When the laminating process is completed, any excess material is removed, at step 810. Finally, electrical terminals are operably connected to the package, as indicated at step 812, if not already attached previously.

Additional structural configurations and implementations of a fleeible PV module of the inventions are discussed below.

Referring to FIG. 9, an embodiment 900 the PV module including a plurality of solar cells (shown as three solar cells 902, 904, and 906) is configured to have angled joints adapted to enhance total internal reflectance (TIR) of light incident onto the module. The solar cells 902, 904, and 906 may be conventional solar cells or solar cells having holographic elements (such as those depicted in FIG. 1, FIG. 2A, and/or FIG. 2B. The solar cells 902, 904, and 906 are encased in an encapsulant 908. In one embodiment, the encapsulant includes a flexible material optionally having an index of refraction between about 1.4 and about 2.0. The top surface 910 of the encapsulant is preferably planar, but may include a non-planar surface. The encapsulated solar cells may form repeat units 912, 914, and 916, as discussed above in reference to FIG. 3. The encapsulant material 908 is configured to define an surface 918 angled or inclined, with respect to the top surface 910, at the edge of each repeat unit of the solar module 300.

The flexibility of the encapsulant 909 enables a flexible and a bendable joint 920 at the intersection of the adjoining repeat units. The joint 920 imparts enhanced flexibility to the solar module 300 in part because of the reduced thickness of the encapsulant layer 908 at the joint.

The angled surfaces 918 of the encapsulate layer enhance the internal reflectance of light within the encapsulant, thereby increasing the amount of light reaching the light-collecting surfaces of the individual solar cells 902, 904, and 906 and, therefore, increasing the energy conversion efficiency of the module. The angle A of inclination of the surface 918 with respect to the surface of a PV cell (or a surface 910 as shown in FIG. 9) is between about 10⁹ and about 70°. It is appreciated that angled surfaces 918 of different individual repeat cells may differ from one another. Generally, the choice of angle A is made such as to maximize the occurrence of the TIR of light within the encapsulant. For example, the angle A for a latitude-mounted solar module may be about 30° to account for the seasonal tilt of the Earth. In another example, the angle A for a vertically—mounted solar module may be about 42°. In yet another example, the angle A for a horizontally mounted solar module may be between about 30° to about 42°.

The angle of inclination A of the end-surface of a repeat solar cell is calculated using Snell's Law based on angles of incidence of light onto the solar module and indices of the material involved. It is appreciated that interplay between the angle A and the critical angle characterizing the TIR of light within the PV module affects whether the light refracted from the incident medium through the top surface 910 of the module towards the angled surface 918 will be totally-internally reflected by the angled surface 918.

Referring now to FIG. 10, a drawing of one repeat unit 1000 showing the refraction of incident light is depicted. The repeat unit 1000 includes a solar cell 1020 encased in an encapsulant 1022 with an angled surface 1024 formed at the bottom portion of the repeat unit 1000 and along the edges of the solar cell 1020. The angled surface 1024 is shown to be at an angle 1028 with respect to the bottom surface of the repeat unit 1000.

The repeat unit 1000 is shown as configured for use on a latitude-mounted solar module. Arrows 1002 represent light incident onto the module 900 at the winter solstice (at an angle 1014 of about −23.5° with respect to a normal). Arrows 1004 represent light incident onto the module at the summer solstice (at an angle 1012 of about 23.5° with respect to a normal).

At the winter solstice, light 1002 striking near the edge 1006 of the individual repeat unit 1000 enters the encapsulate and is refracted at angle 1008 and reflected at an angle 1010 upon striking the angled surface 1024. If angle 1010 is greater than the critical angle, the TIR occurs and the light is fully reflected back into the encapsulant.

Similarly, at the summer solstice, light 1004 striking near the edge 1030 of the individual repeat unit 1000 enters the encapsulant. The light is refracted at angle 1032 upon entering the encapsulant and reflected at an angle 1034 upon striking the angled surface 1024. If the angle 1034 is greater than the critical angle, the TIR occurs and the light is fully reflected back into the encapsulant.

Referring now to FIG. 11, another embodiment 1100 of a solar module having a surface topography on both the upper and lower surfaces is depicted. The solar module 1100 includes a plurality of repeat PV cell units 1108, 1110, and 1112. Each repeat unit is associated with a corresponding solar cell (1102, 1104, 1106). The solar cells 1102, 1104, and 1106 are encased in an encapsulant 1114, optionally formed from a flexible material. In one embodiment, the encapsulant has an index of refraction of about 1.5.

Angled surfaces 1116 are formed on the lower surface of the solar module 1100. The angled surfaces 1116 are configured at an angle (shown, for one of the angled surfaces, to be an angle 1118). (It is appreciated that, in general, different angled surfaces 1116 of the module may be inclined at different angles.) In one embodiment, the angle 1118 is selected based on the operational configuration of the solar module, for example to increase the amount of light that is reflected according to TIR effect within the module. As discussed above in reference to FIG. 10, at least one of the angled surfaces 1116 may be configured as part of a joint between the adjacent PV-cell-units (for example, of a joint between the units 1108 and 1110) to increase the flexibility of the solar module 1100.

As shown in FIG. 11, the upper surface 1120 of a given solar cell unit is specifically formatted to have a dome-like cover or volume 1122 spatially aligned with the corresponding unit. Considering a single individual unit for a moment (for example, the unit 1108), the outer surface 1120 of the encapsulant on the side of the unit opposite to the side containing an angled surface 1116 is adapted to ensure that the thickness of the encapsulant layer is at a maximum substantially over the center of the solar cell (cell 1102 in this case) and gradually decreases toward the edge of the solar cell. Generally, the thickness of the encapsulant portion centered on the solar cell is substantially constant along a first direction and decreases towards the edge of the solar cell when followed along a second direction that is perpendicular to the first direction. In one embodiment, the volume 1114 of the encapsulant associate with the unit 1108 or any other of the volumes 1122 includes a half-cylindrical volume formed over each of the solar cells of the module. Alternatively, any of the volumes 1122 may be shaped and/or sized as a pyramid (having, for example, 3 to 8 substantially planar facets) formed over each solar cell. The volumes 1122 of encapsulant formed over each of the solar cells 1108, 1110, and 1112 are generally configured to focus sunlight striking the outer surface 1120 of the solar module 1100 onto the solar cells 1108, 1110, and 1112.

The topography of the bottom surface 1126 and the top surface 1122 of the solar module 1100 can be defined, for example, using casting or molding. The channels or troughs 1124 are formed in the topography of the top surface 1120 at the boundary of an individual cell units to remove and channel rain water or debris falling onto the latitude-mounted PV module, thereby washing away any dirt and grit that accumulates on the surface 1120.

In a related implementation, the degree of curvature of the surface 1120 over the outer portions of the solar cells is varied depending on the location along the surface 1120 such as to increase the amount of light directed to the solar cells when the incident light is at an extreme angle of incidence and where the central radius of curvature results in non-optimal results (i.e., angular misalignment). In other embodiments, the portion(s) of the volume(s) 1122 over the outer portions of the solar cells are configured to have a linearly tapered region (not shown) to mitigate the angular misalignment of the encapsulant with respect to the solar cells, which may occur during the fabrication of the module.

In embodiments where the structures 1122 includes curved surfaces (such as, for example, dome- and cylindrically-shaped surfaces), radii of curvatures are chosen to maximize efficiency of delivery of incident light to the solar cells during different times of the day. For example, the sun moves during the day at 15 degrees per hour. The radius of curvature is selected accordingly to maximize efficiency for period of time where maximum efficiency is desired. In one embodiment, a surface 1120 includes a parabolic surface.

Referring to FIG. 12, a embodiment of Applicants' solar module 1202 is depicted with an outer surface 1204 of the encapsulant volume 1206. Lines and/or surfaces 1210 that are drawn to be tangential to the surface 1204, in the cross-sectional xy-plane at the points defining the trough(s) 1214, form a dihedral angle 1220 characterizing a degree of curvature of the surface 1204 with respect to the trough(s) 1214. In one embodiment, the surface 1204 is structured to define a dihedral angle 1220 of about 120 degrees such that the surface 1204 forms an angle of about 60° with respect to the solar cell at the edge of each repeat unit. This embodiment is configured to operate efficiently for about 8 hours per day.

In a related embodiment (not shown), and in further reference to FIG. 12, the angle 1220 is about 90° such that the surface 1214 forms an angle of about 45° with respect to the solar cell at the edge of each repeat unit. This embodiment is configured to operate efficiently for about 6 hours per day.

In another embodiment (not shown), and in further reference to FIG. 12, the angle 1220 is about 60° such that the surface 1214 forms an angle of about 30° with respect to the solar cell at the edge of each repeat unit. This embodiment is configured to operate efficiently for about 4 hours per day.

In yet another embodiment (not shown), and in further reference to FIG. 12, the angle 1220 is about 30° such that the surface 1214 forms an angle of about 25° with respect to the solar cell at the edge of each repeat unit. This embodiment is configured to operate efficiently for about 2 hours per day.

It is appreciated that, while not shown in FIGS. 11 and 12, the immediately adjacent PV-cell units in any of the embodiments of FIGS. 11, 12 are operably connected by electrically conductive connectors passing through joints connecting these immediately adjacent PV-cell based units, in a fashion described in reference to FIG. 3, for example.

While the preferred embodiments of the present invention have been illustrated in detail, it should be apparent that modifications and adaptations to those embodiments may occur to one skilled in the art without departing from the scope of the present invention. 

What is claimed is:
 1. A flexible photovoltaic (PV) module, comprising: a plurality of PV cell based units, each unit containing a corresponding PV cell; and a flexible joint connecting a pair of immediately adjacent PV cell based units from said plurality.
 2. A flexible PV module according to claim 1, further comprising an electrically-conductive member electrically connecting said pair of immediately adjacent PV cell based units, said member passing through the flexible joint.
 3. A flexible PV module according to claim 2, wherein said electrically-conductive member includes a flexible conductive tape.
 4. A flexible PV module according to claim 3, wherein at least one of the PV cell based units further comprises a first rigid layer disposed substantially parallel to a surface of the corresponding PV cell.
 5. A flexible PV module according to claim 1, further comprising an optically transparent protective material embedding said pair of immediately adjacent PV cell based units and the flexible joint.
 6. A flexible PV module according to claim 5, wherein a portion of said optically transparent material covering a PV cell based unit has a non-uniform thickness across said PV cell unit.
 7. A flexible PV module according to claim 5, wherein an outer surface of a portion of said optically transparent material forms a dome over a corresponding PV cell based unit.
 8. A flexible PV module according to claim 5, wherein a curvature of said dome changes across a surface of the dome.
 9. A flexible PV module according to claim 5, wherein said optically transparent material has a first surface that is substantially parallel to a surface of a PV cell, and wherein the flexible joint includes a second surface that is inclined with respect to the first surface.
 10. A flexible PV module according to claim 1, further comprising parallel bussing electrically connecting first and second PV cell based units from said plurality.
 11. A flexible PV module according to claim 1, wherein a PV cell based unit includes a hologram.
 12. A flexible photovoltaic (PV) module, comprising: a plurality of PV cell based units, each unit containing a corresponding PV cell; a flexible joint connecting immediately adjacent PV cell based units from said plurality, said flexible joint having a surface that is inclined with respect to a surface of a PV cell; and an electrically-conductive member electrically connecting said immediately adjacent PV cell based units, said member passing through the flexible joint.
 13. A flexible PV module according to claim 11, further comprising an optically transparent protective material embedding said immediately adjacent PV cell based units and the flexible joint such as to define a convex surface substantially centered with respect to a PV cell based unit.
 14. A flexible PV module according to claim 13, wherein said convex surface has a curvature parameter that is varied across said convex surface.
 15. A flexible PV module according to claim 11, wherein at least one of the PV cell based units further comprises at least one of a first rigid layer disposed substantially parallel to a surface of the corresponding PV cell and a hologram. 